The present invention relates generally to a control system for a variable damper in an automotive vehicle suspension system, which adjusts the damping force to be produced depending upon preselected vehicle driving conditions. More specifically, the invention relates to a suspension control system which detects vehicular steering operations and controls the damping force so as to provide the vehicle satisfactory roll-stability.
Published Japanese Patent Application (Tokkai) No. Sho. 56-42739 discloses a suspension control system which controls the damping force produced in response to rolling forces depending upon vehicle speed and steering adjustments. The damping force is so controlled as to be HIGH when the vehicle speed is higher than a set speed and the steering adjustments through greater than a predetermined angle are performed. In addition, the owner of the present application has already disclosed a suspension control system in Published Japanese Utility Model Application (Jikkai) No. Sho. 56-147107. In this system, the damping force produced by a suspension shock absorber is adjusted between HIGH and LOW levels depending upon the vehicle speed, the magnitude of steering adjustments and the angular velocity of steering adjustments.
The rolling force on the vehicle varies with the centrifugal force on the vehicle during cornering, lane changes, curves and so forth. The magnitude of the centrifugal force varies with the vehicle speed and the steering angle. Thus, the rate of change of the centrifugal force depends on the vehicle speed and rate of change of steering angle as well as the vehicle acceleration and the steering angle. For instance, when the vehicle speed is relatively low, the vehicle will tend to roll only when the rate of change of steering angle is relatively high, i.e. when the steering wheel is abruptly turned. On the other hand, when the vehicle is travelling at a relatively high speed, the rolling force on the vehicle can be quite large even in response to a relatively low rate of steering angle adjustment.
In the prior art, since the switching point of damping force between HIGH and LOW levels is determined by reference to a fixed threshold speed, the damper force will not always be suited to driving conditions. Even controlling change-over of the damping characteristics on the basis of the vehicle speed and steering angle itself may allow the damper to unnecessarily stiffen despite a small rolling moment.